The present invention relates to supersonic airplanes and turbine engines for such airplanes, and more particularly to a single spool turbine engine designed to provide a predetermined amount of thrust at a given throttle setting when propelling an airplane at a predetermined supersonic Mach number, to a method for operating such an engine, and to an airplane designed for such an engine.
A conventional turbojet engine is designed to provide maximum thrust at sea level under static operating conditions, that is, such engines have a sea level static (SLS) design point. The maximum thrust that can be derived from a conventional turbojet engine at an intermediate throttle setting (a predetermined high throttle setting without afterburning) is limited by the turbine inlet temperature, other internal engine operating parameters, and limitations imposed by engine construction materials and techniques. The corrected airflow through the conventional turbojet engine with a sea level static design point is maintained at the maximum allowable value from static conditions through transonic flight speeds. Increases in the flight Mach number beyond transonic flight speeds will cause the engine corrected airflow to lapse, that is, drop significantly at an almost exponential rate, as the flight Mach numbers increase linearly above the transonic flight regime. The lapse in corrected airflow through the conventional turbojet engine begins when the turbine inlet temperature rises to its maximum allowable level. Thereafter, increasing compressor inlet temperatures associated with the increased flight Mach number requires a reduction in fuel flow to the engine, causing the compressor corrected rotor speed and corrected airflow to decrease while the turbine inlet temperature remains constant at its maximum allowable value.
The significant decrease in corrected airflow through a conventional sea level static (SLS) design engine at supersonic Mach numbers will cause a corresponding drop in the net thrust derivable from the engine at supersonic Mach numbers. In order to obtain the required amount of thrust from a conventional turbojet engine operating at supersonic Mach numbers, the engine must be overdesigned to provide adequate thrust at supersonic Mach numbers, yielding an engine that is grossly overdesigned for the subsonic and transonic flight regimes. Such an overdesigned conventional engine is characteristically large and heavy, both of which characteristics are undesirable. An alternative to overdesigning the engine is to provide the engine with an afterburner, thus providing an augmented power setting to achieve the thrust required for driving an airplane at supersonic Mach numbers. An augmented power setting, however, significantly increases the specific fuel consumption of the engine (pounds of thrust per pound of fuel per hour consumed, hereinafter referred to as SFC). To achieve fuel efficient supersonic flight speeds, however, it is desirable to operate an engine at an intermediate power settings (that is, a nonaugmented power setting) rather than a partially or fully augmented power setting, thereby lowering the SFC at supersonic speeds.
It is a broad object of the present invention to provide a turbojet engine that can provide adequate thrust and associated low specific fuel consumption at supersonic flight speeds. Additional objects of the present invention are to provide such an engine that is simple in design and relatively inexpensive and that has high reliability and low maintenance; to provide such an engine that will yield the desired thrust at intermediate (nonaugmented) throttle settings at supersonic flight speeds; to provide such an engine that has adequate nonaugmented transonic thrust to provide acceptable acceleration through the transonic flight regime so that the supersonic flight speeds can be achieved in a reasonable time interval; to provide such an engine that can be manufactured with current state of the art engine technology and materials; and, to provide such an engine that generally has the same size and weight as the conventional SLS designed afterburning turbojet engines.
Another broad object of the present invention is to provide an airplane and associated inlet and exhaust nozzle configurations that are relatively simple, that require no variable geometry engine inlet structure or variable geometry nozzle structure for intermediate throttle settings and that enhance the operating characteristics of the turbine engine employed to drive the airplane; and to provide an airplane that can economically cruise at supersonic flight speeds and that has the capability to reach such speeds in a reasonable time.